The present invention generally relates to processing a photoresist clad semiconductor substrate. In particular, the present invention relates to cleaning a semiconductor substrate having a patterned photoresist thereon using vapor drying techniques.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This includes the width and spacing of conductive features and the surface geometry such as corners and edges of various features.
The requirement of small features (and close spacing between adjacent features) requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, X-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the photomask, for a particular pattern. The lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. Exposure of the coating through the photomask causes a chemical transformation in the exposed areas of the coating thereby making the image area either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Patterning a photoresist over a semiconductor substrate is typically followed by a deionized water rinse, which is then followed by a spin-drying step. However, there are three notable problems associated with water rinse and spin-drying patterned photoresist clad structures.
One problem is the formation of watermarks on the surface of the patterned photoresist clad structures. Watermarks typically form when dissolved, non-volatile material (such as silica and other dissolved contaminants) precipitate out of the deionized water as it evaporates from the surface of the structure. The presence of watermarks on a semiconductor structure may create difficulties in subsequent manufacturing processes. Watermarks, which can be as small as 1 to 10 xcexcm and laden with particulate matter, are difficult to prevent and/or remove. As feature sizes continue to shrink, surface tension between the liquid and the device features on the semiconductor structure increases, so watermarks are created more easily.
Another problem with spin dryers is the possible charging of patterned photoresist clad structures which causes them to attract particles upon exposure to a cleanroom. Spin rinse dryers provide an ideal environment for static charge generation and build-up. In a spinning chamber, highly insulative deionized water shears across photoresist and silicon and surfaces (and other insulative materials), creating high levels of static charge. Although static charges are generated inside most semiconductor process tools, higher levels typically occur in spin rinse dryers. Charged structures leaving the spin rinse dryers immediately attract and bond particles and other airborne contaminants on their surfaces.
Yet another problem with spin dryers is the damage caused by the large shear forces. In particular, the features of the patterned photoresist (such as lines and mesas) may break or become damaged under the shear forces from spinning. And as feature sizes decrease, the mechanical stability of the features decreases. This is especially true for high pitch features and fine line lithography. The continuing trend toward higher device densities leads to more damage caused by the large shear forces.
Attempts to solve the three aforementioned problems associated with spin drying involve the use of isopropyl alcohol. In one such technique, the water on the surface of the wafer is displaced by isopropyl alcohol before the water has a chance to evaporate, and then the alcohol is evaporated from the surface of the wafer. Another technique, called vapor drying, involves condensation of isopropyl alcohol vapor onto the surface of the wafer, causing the water present on the wafer to be taken up by the dry alcohol. The water-rich alcohol then drips off of the wafer before water evaporation can occur, and is replaced by more dry alcohol condensate, which is then evaporated.
Isopropyl alcohol vapor drying is frequently employed to clean inorganic surfaces on semiconductor structures. Inorganic surfaces include those made of silicon dioxide, silicon nitride, polysilicon, amorphous silicon, metals, metal nitrides, metal suicides, and the like. However, the use of isopropyl alcohol vapor drying on patterned photoresist clad semiconductor structures often results in damage to the photoresist pattern. This is believed attributable to undesirable interaction between isopropyl alcohol and the organic photoresist material. Accordingly, there is an unmet need for methods and systems that improve lithography, and in particular, improve the cleaning of patterned photoresist clad semiconductor structures without degrading the photoresist pattern.
The present invention provides systems and methods for cleaning patterned photoresists using an alcohol vapor. The alcohol vapor cleans and dries the patterned photoresist while minimizing or eliminating the removal or destruction of the pattern, as well as minimizing the formation of watermarks on the photoresist. The shear forces associated with spin drying, that may remove, damage or break the pattern are also eliminated by the present invention.
One aspect of the present invention relates to a method of cleaning a patterned photoresist clad structure involving the steps of contacting the patterned photoresist clad structure with an alcohol vapor comprising at least one compound having the Formula ROH, wherein R is a hydrocarbon group comprising from 4 to about 8 carbon atoms; condensing the alcohol vapor on the patterned photoresist clad structure; and removing the condensed alcohol vapor from the patterned photoresist clad structure.
Another aspect of the present invention relates to a method of cleaning a patterned photoresist clad structure involving the steps of contacting the patterned photoresist clad structure with a vapor comprising an organic compound having a boiling point from about 102xc2x0 C. to about 175xc2x0 C.; condensing the vapor on the patterned photoresist clad structure; and removing the condensed vapor from the patterned photoresist clad structure.
Yet another aspect of the present invention relates to a method of cleaning a patterned photoresist clad structure involving the steps of contacting the patterned photoresist clad structure with a vapor comprising an organic compound having a flash point from about 15xc2x0 C. to about 80xc2x0 C.; condensing the vapor on the patterned photoresist clad structure; and removing the condensed vapor from the patterned photoresist clad structure.